The promise of hypersonic flight sending us halfway around the
world in a matter of hours is being bandied about again, this time by a British
company that declares, with all due humility, that it has made “the biggest
breakthrough in aerospace propulsion technology since the invention of the jet
engine.”

Reaction Engines Limited says its hypersonic engine will send
us streaking across the sky at speeds well over Mach 5, allowing us to have
bagels for breakfast in New York and sushi for lunch in Tokyo. The hypersonic
engine design reportedly includes new ways of cooling the air for an engine that
will use oxygen in the atmosphere up to Mach 5.5 before switching to rocket
power for the ride in space.

Hypersonic flight
has long topped the list of dreamy
aerospace ideas. The military loves the idea of super-fast
missiles and even bombers,
while the rest of us dream of flying from the Big Apple to Tokyo in just a few
hours. The big problem has been propulsion. At speeds beyond Mach 2 or so, a jet
engine has trouble getting the oxygen needed for combustion. It’s sorta like
trying to take a deep breath by sticking your head out the window at 200
mph.

Solving this problem
is not impossible, but neither is it terribly practical. Kelly Johnson’s SR-71
Blackbird design used very creative ways to handle
the incoming air needed to achieve a record-setting Mach 3+ speeds. But past
that it gets really tough, and dealing with all that heat poses another
challenge.

So far, only rocket engines have been capable of practical
hypersonic flight, but the vehicles that use them require multiple stages to
reach space. To avoid the cumbersome need to carry a supply of oxygen, as is
done on rockets and was used by the space shuttle, engineers have struggled with
an air-breathing design that can operate in the hypersonic speed range as a
first stage.

Reaction Engines claims it’s cracked the problem with a design
that could allow a vehicle to take off, reach orbit using a combination of an
air-breathing engine and rocket, then return to Earth. The secret is cooling the
air as it enters the hypersonic SABRE engine.

“[The] pre-cooler technology is designed to cool the incoming
airstream from over 1,000 Celsius to minus 150 Celsius in less than 1/100th of a
second, without blocking with frost,” the company claimed in its press
release.

It’s a promising design that tackles one of the bigger
problems facing hypersonic engines: the enormous amount of heat generated when
you compress air at extremely high speeds. The air-breathing engine will
accelerate a vehicle to about Mach 5.5, according to the company, after which a
liquid oxygen tank will supply a rocket engine for the portion of the flight in
space. But unlike current space vehicles, there will only be one stage involved
for the entire flight thanks to the boost from the SABRE design.

The European Space Agency says it has evaluated the pre-cooler
design and says it is satisfied that the design should move forward. The agency
is negotiating a contract to help support the further development of Reaction
Engines’ design.

Reaction Engines
said it has completed more than 100 test runs of the cooling system and it hopes
to have a sub-scale ground engine running by 2015. But as the X-51 Waverider team has
discovered, it’s a long road, er, flight from a new component breakthrough
to hypersonic flight.